beta-Adrenergic induced K+ current in Xenopus oocytes: role of cAMP, inhibition by muscarinic agents

The K+ current induced by isoprenaline acting on beta-adrenergic receptors in Xenopus laevis has been studied in oocytes still surrounded by their follicular cells and inner ovarian epithelium. Forskolin, an adenylate cyclase activator, induced a similar K+ current and when used at subliminal concentration it potentiated the current induced by isoprenaline. Inhibition of phosphodiesterase by methylisobutylxanthine also enhanced the response to isoprenaline. 8-Br-cAMP, a permeant analogue of cAMP also produced a K+ current. Acetylcholine produced a long lasting inhibition of the isoprenaline current. This inhibition was not seen in the presence of atropine. It is concluded that the K+ current induced by the activation of beta-adrenergic receptors in the oocyte is mediated by an intracellular rise of cAMP.